1. Field of the Invention
This invention relates to a hub driving assembly for a hub of a bicycle, more particularly to a hub driving assembly which is adapted to be connected to a sprocket of a bicycle to transmit a driving force from the sprocket to rotate a hub.
2. Description of the Related Art
Referring to FIG. 1, a conventional bicycle hub assembly is shown to include a hub 2 mounted on and rotatable relative to an axle 1, and a driving unit 3 disposed to uni-directionally transmit a driving force to rotate the hub 2. The hub 2 has an inner tubular wall 201 and a toothed member 202 disposed in the inner tubular wall 201. The driving unit 3 is mounted on and is rotatable relative to the axle 1. Referring to FIGS. 2 and 3, the driving unit 3 includes a sprocket-mounting cylinder 301, a plurality of pawls 302, and a plurality of biasing members 303. The cylinder 301 has an outer cylindrical surface 306 which extends along an axis of the axle 1 to terminate at a tubular end surface 305, and a plurality of angularly-displaced retreat bores 307 which extend respectively and axially from the tubular end surface 305. The cylinder 301 is formed integrally with a sprocket 304 for receiving a driving force therefrom. The pawls 302 and the biasing members 303 are disposed respectively in the retreat bores 307. Each of the pawls 302 is movable by the biasing action of the respective biasing member 303 to a driving position, where the pawl 302 extends radially and outwardly for meshing with the toothed member 202 (as shown in FIG. 1) such that the driving force is transmitted to rotate the hub 2 when the sprocket is rotated in a driving direction (i.e. a counterclockwise direction as shown in FIG. 3).
Although the driving unit 3 can transmit the uni-directional driving force to the hub 2, the following drawbacks arise:
1. The pawls 302 and the biasing members 303 may be moved axially and may thus slip from the retreat bores 307 through access openings 308 in the tubular end surface 305 before the driving unit 3 is fitted in the hub 2, thereby resulting in inconvenience during assembly.
2. Even after the assembly of the driving unit 3 to the hub 2 is completed, the pawls 302 may move freely in the retreat bores 307 and are partially exposed to the access openings 308, thereby resulting in reduced driving force.
3. As the pawls 302 and the biasing members 303 may move freely in the retreat bores 307, the service life thereof is shortened.